We propose to develop an optical detection scheme for the real-time detection and recognition of single viruses and larger proteins. Viruses are responsible for a considerable number of human diseases such as chickenpox or the common flu. In some cases (Ebola, AIDS, SARS,) viral pathogens result in serious disease or even death. There is a growing need to rapidly and accurately quantify viruses but the detection and isolation of viruses remains a time-consuming laboratory procedure. The proposed detection scheme makes use of background-free optical detection in nanofluidic channels. In this method, a solution with target viruses is transported along a nanofluidic channel using electro osmotic flow. A laser beam is focused into the channel and the backscattered light from individual particles is recombined with a reference beam and then interferometrically measured with a split detector. This scheme eliminates the problem of background scattering and laser power fluctuations. In its preliminary configuration the particle detector is capable of detecting, within a time of one millisecond, single Influenza, Sindbis (alpha), and HIV virions, as well as polystyrene particles down to 15 nanometers in size. Despite of its high sensitivity, the detector is currently not able to identify the nature of a detected particle. For example, a target virus could generate the same signal as a carbon particle of different size. In order to discriminate target viruses against other particles and also to differentiate different virus types from each other we propose to implement multicolor heterodyne detection. While heterodyning removes noise due to phase variations, multicolor operation allows us to eliminate the dependence on particle size and to obtain a chemically-specific fingerprint for the viruses to be recognized. In this project we will demonstrate the detection and recognition of single viruses within a time of less than one millisecond. The detector will be tested and characterized with intact viruses (Parainfluenza, Papilloma, Herpes Simplex, Vaccinia, Influenza X31, Sindbis (alpha), Adeno, HIV) supplied by collaborators. PUBLIC HEALTH RELEVANCE: The ability to detect and identify single viruses is important for determining the viral load in infected individuals and to understand how the immune system clears a virus infection. This will allow us to address important biomedical questions and to design more rational vaccination and treatment strategies. The detection of single viral pathogens is of equal importance for public health and public safety.